The present invention relates to a structure of an aberration corrector used for a charged particle beam apparatus, and a charged particle beam apparatus equipped with the aberration corrector.
In the charged particle beam apparatuses, such as the scanning electron microscope, the scanning transmission electron microscope, the transmission electron microscope, and the focused ion beam machining system, multipole (dipole, quadrupole, octapole, etc.) have been used for the deflector and the astigmatism corrector. In recent years, in order to correct spherical aberration and chromatic aberration of an objective lens with axially rotational symmetry, the aberration corrector made by combining the quadrupole, hexapole, octapole, etc. has been proposed and developed. Actually in 1995, it was shown by Haider et al. that the spherical aberration can be corrected in the TEM, and it was shown by Zach et al. that the chromatic aberration and the spherical aberration can be corrected in the SEM (for example, see H. Rose, Optik 33 (1971) pp. 1-24 and J. Zach and M. Haider, Nuclear Instruments and Methods in Physical Research, A363 (1995) pp. 316-325). In these aberration correctors, it is required that a multipole field that is a high-precision superposition of fields is formed in an area through which a charged particle beam passes. As means for actually implementing such a multipole field, there is no method except arranging multipole for forming the multipole field on the same axis so as to be in a multistage structure at present. Therefore, all the aberration correctors currently manufactured have a configuration where multipoles are arranged in a multistage structure.
The conventional multipole mainly include: the magnetic field type multi-magnetic pole that is intended to be used in the spherical aberration correctors for TEM and STEM, the EELS apparatus, etc.: the electrostatic type multipole that is used for electrostatic deflection in the SEM, the electron beam lithography system, etc. and the electrostatic-magnetic field superposition type multipole for chromatic and spherical aberration corrector. Magnetic poles do not need to be exposed in a vacuum passage of the charged particle beam, whereas in the electrostatic type or electromagnetic multipole, poles need to be exposed, and therefore the latter is sensitive to dirt and protrusions on the surface of poles. Moreover, the electromagnetic multipole needs to have a complicated configuration, such as a fact that each pole is insulated from other poles electrically and each pole is connected magnetically to the other poles with a yoke, so that electromagnetic poles constitute a magnetic circuit. What is commonly required for these is excellent accuracy in assembling the multipoles, capability for generating a multipole field with sufficient symmetry, and high-precision coincidence of a mechanical axis of an upper multipole and a lower multipole, and a phase around the axis when a multistage configuration is adopted. From a viewpoint of mass productivity, it is mentioned that parts and adjustment locations are fewer in number and an adjustment work is simple. However, at present, a manufacture method for manufacturing the aberration corrector that satisfies both mass productivity and the assembly accuracy has not been established.
JP-A-2004-234961 discloses a magnetic multipole such that a yoke for connecting a magnetic pole and a magnetic pole is integrated into a single piece by wire electrical discharge machining. Moreover, this patent document (JP-A-2004-234961) shows 1) an electrode aligning and fixing method by plural pins, and 2) electrode aligning and fixing method using a high-precision cylinder. Moreover, JP-A-2004-241190 discloses a method for manufacturing multipole by fixing uncut multipole with a screw, and after that cutting the uncut portion.